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Use of the Estimated Average Glucose (eAG) in Patient Care

Use of the Estimated Average Glucose (eAG) in Patient Care. A Typical Patient Encounter.

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Use of the Estimated Average Glucose (eAG) in Patient Care

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  1. Use of the Estimated Average Glucose (eAG) in Patient Care

  2. A Typical Patient Encounter “So, Mrs. Smith, it looks like you do have diabetes. Your repeat fasting blood sugar was 178, and as you recall the first one was 187. Over 126 is diabetes. Also, your hemoglobin A1c was way too high at 8.6%. Normal is less than 6%. We need to get it below 7%.”

  3. A Typical Patient Encounter “What’s a hemoglobin A…whatever you said? I remember my hemoglobin was low when I was pregnant. What were those other numbers? What do you mean, 7%...of what?”

  4. G G G G G G G G G G  G __% = G G G G

  5. Uh… ???

  6. It’s Not Just Confusing forNewly Diagnosed Patients • High levels of testing of HbA1c for patients with known diabetes (> 90%). • Of patients with test in past 6 months: • 66% did not know result • 25% accurately reported within 1% range (< 7%, 7-8%, 8-9%) • 9% inaccurately reported within 1% range Heisler, Diabetes Care 28:816,2005

  7. The Clinical Dilemma • HbA1c: useful for research, risk prediction, target of therapy • Well standardized • HOWEVER, difficult to explain to patients • Concept of % is not intuitive • Glucose more familiar to patients from self-monitoring or from laboratory glucose results

  8. The Concept of Average Glucose • We tell patients the HbA1c reflects their “average glucose over 2-3 months” • But: do we know this for sure?

  9. The A1C-Derived Average Glucose (ADAG) Study International study designed to: • Carefully look at relationship between HbA1c and average glucose • Determine the mathematical relationship between the two for reliable conversion • Establish that the relationship is valid across: - Diabetes types - A wide range of HbA1c levels and age - Different races/ethnicities Nathan et al, Diabetes Care 31:1473, 2008

  10. Cameroon Denmark Italy The Netherlands United States Boston New York San Antonio Seattle India (site dropped due to specimen handling issues) ADAG Study Centers

  11. Participants in ADAG • Goal was to recruit people with • Type 1 diabetes • Type 2 diabetes • No diabetes • With a range of • Ethnicity/race • HbA1c levels • Excluded those with conditions that would interfere with measurement/interpretation of HbA1c or glucose

  12. Measures of Glycemia in ADAG Study • CGM (calibrated by 8-point glucose profiles with Hemocue meter) for at least 48 hours at baseline and every month for 3 months • 7-point glucose profiles for 3 days per week with One Touch Ultra meter • HbA1c at baseline and monthly X 3 months with DCCT-aligned assay in a central laboratory • Four measures of HbA1c to assure stable control, but only final value used for correlation with prior 3 months’ glucose readings

  13. ADAG Study Flow • Total Enrolled 661 • Eliminated from analysis 154 (23%) • - Dropped out or excluded 91 (14%) • during study • - Inadequate CGM 11 (2%) • - Inadequate HbA1c samples 52 (8%)

  14. Baseline Characteristics of ADAG Participants

  15. Normal D i a b e t i c ADAG Study: Distribution of Baseline HbA1c 44% Number of subjects 38% 18% Baseline HbA1c (%)

  16. ADAG Study: Glucose Monitoring • CGM – mean of ~ 2,400 measurements per participant • LifeScan meter ~ mean of 300 measurements per participant • Mean of ~ 25 measurements per week • Goal was a minimum of 21 tests per week • Total ~ 2,700 measurements/participant during 12 weeks

  17. ADAG Study: Analyses • CGM results corrected upward by 5% to be consistent with BG • Each glucose measure weighted in proportion to the inverse of total number of measurements on that day (each day had equal weight) • Arithmetic mean glucose calculated for each participant • Linear regression model used to estimate relationship between average glucose and the 3-month HbA1c

  18. 90% of cohort values fall in this range Calc. AG (mmol/L) ADAG Study: Study Success 90% of values fell within +/- 15% HbA1c (%)

  19. ADAG Study: Correlation of AG With HbA1c AG (mg/dl) = 28.7 x HbA1c – 46.7 R2 = 0.84 P < 0.0001 AG (mg/dl) HbA1c (%)

  20. ADAG Study: Correlation of AG with HbA1c: CGM data vs. Meter No difference in relationship (P=0.18) whether LifeScan or CGMS data used HbA1c (%)

  21. ADAG Study: Other Factors Examined • Does the HbA1c-Average Glucose relationship differ by: - Type 1 or type 2 diabetes NO - Diabetes or no diabetes NO - Amount of glucose variability NO - Gender NO - Age NO - Ethnicity/Race NO (but trend toward higher HbA1c per AG in African and African-American participants vs. whites, P=0.07) - Smoking NO

  22. ADAG Study Excluded Known Sources of “Inaccuracy” of HbA1c • Hemoglobinopathy • Anemia • Pregnancy • Hepatic or renal disease • Etc.

  23. ADAG Study Conclusion: HbA1c Correlates Highly With AG 450 400 AG (mg/dl) = 28.7 x HbA1c – 46.7 350 300 AG (mg/dl) 250 200 150 100 50 3 4 5 6 7 8 9 10 11 12 13 Measured HbA1c (%)

  24. Implications • Tight correlation between HbA1c and AG allows us to translate HbA1c into an estimated Average Glucose (eAG) • eAG will apply to the majority of patients with diabetes • Barring “traditional” conditions interfering with the assay or the relationship between glycemia and HbA1c

  25. ADAG Study: “Translation” of HbA1c into eAG • eAG • HbA1c (%) (mg/dl) (mmol/l)_ • 5 97 5.4 • 6 126 7.0 • 7 154 8.6 • 8 183 10.2 • 9 212 11.8 • 10 240 13.4

  26. Note that the numbers are different • ADAG DCCT • HbA1c (%) (mg/dl)___(mg/dl)______ • 6 126 135 • 7 154 170 • 8 183 205 • 9 212 240 • 10 240 275

  27. Consensus Statement FCC, EASD, IDF, ADA Sept 2007) • HbA1c assay to be standardized worldwide using the new IFCC standard and expressed as: • % as currently used (DCCT values) • IFCC units in mmol HBA1c/mol HbA • eAG in mmol/l or mg/dL (if ADAG study meets its data acceptability goals) • This paved the way for reporting both HbA1c and EAG on lab reports Diabetes Care and Diabetologia, 2007

  28. What Won’t Change…And What’s New • To a clinician, there is no change in the HbA1c assay • To clinical chemists, there is a new IFCC standard in the background • We have the potential for a valuable educational tool for patients

  29. A Typical Patient Encounter “So, Mrs. Smith, it looks like you do have diabetes. Your average blood sugar is around 200. When people don’t have diabetes, this number is below 125. We need to work with you to try to get this number, the average glucose, down below 150 over the next few months with some weight loss, exercise, and a medication. Let’s talk some more about what you can do…”

  30. A Typical Patient Encounter “Wow, I’m not happy to hear that…I know that diabetes can do some bad things. Tell me what I can do to get my average glucose down.”

  31. What is ADA Doing to Promote Use of eAG in Patient Care? • Health care provider education • ADA Scientific Sessions, June ’08 • American Association of Clinical Chemists, August ‘08 • AADE Annual Meeting, August ‘08 • eAG calculators (handheld and on professional.diabetes.org) • Patient education • Website • Diabetes Forecast magazine, books • Pamphlets and brochures • ADA will include term “average glucose” in all consumer pieces

  32. What Can Clinicians and Educators Do? • Choose which term—A1C or Average Glucose—to use with each patient (some may already be used to A1C) • In verbal communications, no need to say “estimated” • We want to keep the A in A,B,Cs • Use updated table, calculator on www.diabetes.org, or other tools to convert A1C to average glucose • “Lobby” your lab to report both numbers

  33. What Can Clinical Chemists Do? • Even with tools, most clinicians will not take the time to calculate conversions • Reporting both HbA1c (DCCT-aligned) AND eAG on lab reports will do the most to promote wide use of the term • Professional and patient education may drive demand • Conversion is a simple regression equation

  34. Average Glucose Blood pressure Cholesterol to help make the “A” understandable!

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